Ultra-low friction configuration

ABSTRACT

Briefly, embodiments of a configuration for ultra-low friction is disclosed

BACKGROUND

This disclosure is related to ultra-low friction, such as, to a configuration that exhibits such friction.

Micro-electromechanical systems are sometimes referred to as MEMS. Such devices, apparatuses and/or systems, for example, typically include parts or one or more portions that move or otherwise function on a scale of size that is around a micron. This type of technology is currently receiving commercial attention. The small size of such devices is at least one advantage. Likewise, work is also being pursued with devices and/or the like on a relatively larger scale or a relatively smaller scale, such as the sub-micron and/or the nanometer scale level, for example. Whether the size of such devices is around several microns, larger, or smaller, it may be advantageous to have the capability to reduce friction that may typically be present.

BRIEF DESCRIPTION OF THE DRAWINGS

Subject matter is particularly pointed out and distinctly claimed in the concluding portion of the specification. Claimed subject matter, however, such as with respect to organization and/or method of operation, for example, together with objects, features, and/or advantages thereof, may be understood by reference to the following detailed description if read with the following accompanying drawings in which:

FIGS. 1-4 are plots illustrating particular examples of force plots of dielectric functions associated with a particular embodiment of a device having ultra-low friction, the particular embodiment being made from particular materials;

FIG. 5 is a schematic diagram of an embodiment of a micro- or nano-compass exhibiting ultra-low friction;

FIG. 6 is a schematic diagram of another embodiment of a device exhibiting ultra-low friction;

FIG. 7 is a plot of dielectric functions for various birefringent materials;

FIG. 8 is a schematic diagram of an embodiment of a system exhibiting ultra-low friction;

FIG. 9 is a table of parameters for various materials that may be employed to compute a dielectric function of those materials; and

FIG. 10 is another table of parameters for various materials that may be employed to compute a dielectric function of those materials.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are set forth to provide a thorough understanding of claimed subject matter. However, it will be understood by those skilled in the art that claimed subject matter may be practiced without these specific details. In other instances, well-known methods, procedures, components and/or circuits have not been described in detail so as not to obscure claimed subject matter.

According to quantum electrodynamics, quantum fluctuations of electric and magnetic fields may give rise to zero-point energy that may remain, even in the absence of electromagnetic sources. See, for example, P. W. Milonni, The Quantum Vacuum: An Introduction to Quantum Electrodynamics (Academic Press, San Diego, 1993). In 1948, H. B. G. Casimir predicted, for example, that two electrically neutral metallic parallel plates in a vacuum, assumed to be perfect conductors, should attract each other with a force inversely proportional to the fourth power of separation. The plates act as a cavity for electromagnetic modes having nodes on both walls. Zero-point energy, per unit area, in this example, if such plates are kept at close proximity to each other, is smaller than if the plates are at infinite separation. The plates thus should mutually attract to reduce energy associated with electromagnetic field fluctuations. This led to a generalized theory regarding isotropic dielectrics by E. M. Lifshitz, I. E. Dzyaloshinskii, and L. P. Pitaevskii (referred to hereinafter as “Lifshitz's theory” or “Lifshitz's equation”) from Casimir's theory. In this latter theory, a force between two uncharged parallel plates with arbitrary dielectric functions may be derived according to an analytical formula that relates the Helmholtz free energy associated with electromagnetic field fluctuations to the dielectric functions of interacting materials and of the medium in which they are immersed. At relatively short distances, such as smaller than a few nanometers, for example, this theory provides a complete description of the non-retarded van der Waals force. At larger separations, however, retardation effects associated with a finite speed of light value may give rise to a long-range interaction that, in the case of two ideal metals in a vacuum, reduces to Casimir's result. Lifshitz's equation also shows that two plates made out of the same material will attract. For slabs of different materials, on the contrary, the sign of the force depends at least in part on dielectric properties of the medium in which they are immersed. While the force is attractive in a vacuum, there may be situations for which a properly chosen liquid or fluid may result in two plates that mutually repel. See, for example, J. Mahanty and B. W. Ninham, Dispersion Forces (Academic Press, London, 1976); J. N. Isrealachvilli, Intermolecular and Surface Forces (Academic Press, London, 1991).

This so-called Casimir-Lifshitz force between dielectrics is now receiving considerable attention. The theory has been verified in several high-precision experiments mainly focused on the interaction between metallic surfaces in a vacuum. Less precise measurements in liquids have also been reported, and experimental evidence for a repulsive van der Waals force between dielectric surfaces in different fluids has also been reported. See, for example, A. Milling, P. Mulvaney, and I. Larson, J. Colloid Interface Sci. 180, 460 1996; A. Meurk, P. F. Luckham, and L. Bergstrom, Langmuir 13, 3896 1997; S. Lee and W. M. Sigmund, J. Colloid Interface Sci. 243, 365 2001. It has also been pointed out that the Casimir-Lifshitz force might be a potentially relevant issue for development of micro- and nano-electromechanical systems. See, for example, H. B. Chan, V. A. Aksyuk, R. N. Kleiman, D. J Bishop, and F. Capasso, Phys. Rev. Lett. 87, 211801 (2001).

As shall be explained in more detail hereinafter, in a suitable environment, it may be possible to employ such a force to reduce friction for systems, devices, apparatuses and/or the like having a size of several microns or smaller, for example. In this context, this type of friction shall be referred to as ultra-low friction. Of course, as is well-understood, typically there is static friction and dynamic friction. It is noted that claimed subject matter includes both ultra-low static friction and ultra-low dynamic friction. As shall be explained in more detail hereinafter, ultra-low static friction refers to static friction that may be reduced to such a relatively small amount that it exceeds the sensitivity of conventional or state-of-the-art sensors. Although claimed subject matter is not limited in scope in this respect, in an embodiment, as described in more detail hereinafter, it is believed that static friction may, in theory, be made arbitrarily small. This would appear to involve a value that is at least smaller than the feasible sensitivity of a sensor employed to measure such friction. For example, in the embodiment described in more detail later, a vertical force, such as weight, is suppressed or counterbalanced. While, theoretically at least, substantially no static friction should be present, practically speaking there may be some small, albeit not feasibly measurable, surface roughness and/or contamination, for example. Likewise, embodiments within the scope of claimed subject matter, such as described in more detail below, also reduce dynamic friction between surfaces. This reduced dynamic friction in this context is also referred to as ultra-low.

From Lifshitz's theory, it is possible to show that the force between two plates with dielectric functions ε₁ and ε₂ immersed in a medium with dielectric function ε₃ is repulsive if, for imaginary frequencies, we have ε₁<ε₃<ε₂ or ε₂<ε₃<ε₁ over a range of frequencies which, at a given distance, substantially dominate the force contribution; likewise, the force is attractive otherwise. See, for example, J. Mahanty and B. W. Ninham, Dispersion Forces, Academic, London, 1976; J. N. Israelachvilli, Intermolecular and Surface Forces, Academic, London, 1991. It is noted that at different distances, different frequencies contribute different amounts to the force.

By way of example, without limiting the scope of claimed subject matter, consider a common combination of materials: Silica-Ethanol-Gold. For example, consider plates made of Silica and Gold separated by Ethanol. As may be seen in FIG. 1, ε_(Silica)<ε_(Ethanol)<ε_(Gold) over a frequency range that, at a particular distance relevant to micro- and nano-devices, for example, substantially dominates the force contribution, which should give a repulsive interaction between Silica and Gold, in this example. Here, E may be determined from optical/spectral experiments; however, for convenience, we also note that dielectric properties of a variety of materials may be described reasonably well by a multiple oscillator model, such as, for example, the so-called Ninham-Parsegian representation; see, for example, the previously cited text, Dispersion Forces. In this example, this representation may be written as follows: ${\varepsilon\left( {i\quad\xi} \right)} = {1 + {\sum\limits_{j = 1}^{N}{\frac{C_{j}}{1 + \left( \frac{\xi}{\omega_{j}} \right)^{2} + \frac{g_{i}\quad\xi}{\omega_{j}}}.}}}$ in which C_(j) is given by (2f_(j))/(πω_(j)), f_(j) is the oscillator strength, ω_(j) is the relaxation frequency multiplied by 2π, and g_(i) is the damping coefficient of the oscillator. For a variety of inorganic materials, two un-damped oscillators, referred to hereinafter as “the two oscillator model,” may be employed with satisfactory results to describe dielectric properties of particular materials, as follows: ${{\varepsilon\left( {i\quad\xi} \right)} = {1 + \frac{C_{IR}}{1 + \left( \frac{\xi}{\omega_{IR}} \right)^{2}} + \frac{C_{UV}}{1 + \left( \frac{\xi}{\omega_{UV}} \right)^{2}}}},$ in which ω_(IR) and ω_(UV) are the characteristic absorption angular frequencies in the infrared and ultraviolet ranges, respectively, and C_(IR) and C_(UV) are the corresponding absorption strengths, for particular materials and for this particular embodiment or example.

However, claimed subject matter is not limited to employing the two oscillator model. For example, the two oscillator model does not always provide a complete description of the dielectric properties of materials; however, in spite of its simplicity, if applied to dispersion effects, it often provides reasonably precise results. Without limiting the scope of claimed subject matter, applying this model to perform calculations allows one to determine the force between these two plates using Lifshitz's theory, as described in more detail hereinafter.

Of course, other models may also be employed. For example, again, without limiting the scope of claimed subject matter, in another embodiment, the so-called Drude model may be employed. This latter model, for example, may be employed to describe dielectric properties of metals, although, again, claimed subject matter is not limited in scope in this respect. FIG. 10 is a table that provides optical parameters found using a Drude Model fit of experimental dielectric functions for a variety of metals. In this context, more optical properties of dielectrics may be found in, for example: Hough and White, Advances in Colloid and Interface Science, 14 3-41 (1980) and Lennart Bergström, Advances in Colloid and Interface Science, 70 125-169 (1997), and references therein. Likewise, properties of many metals may be found in the following: M. A. Ordal, et al papers: Applied Optics 22, 1099 (1983); Applied Optics 26, 7449 (1987); Applied Optics 27, 1203 (1988).

Applying for this embodiment the two oscillator model provides the force between the plates as: ${F\left( {d,T} \right)} = {\frac{\partial}{\partial d}\frac{k_{B\quad}T}{8\quad\pi\quad d^{2}}{\sum\limits_{n = 0}^{\infty}{\int_{r}^{\infty}{x\quad{\mathbb{d}x}\left\{ {{\ln\left( {1 - {\Delta_{31}^{R}\quad\Delta_{32}^{R}\quad{\mathbb{e}}^{- x}}} \right)} + {\ln\left( {1 - {\overset{\_}{\Delta_{31}^{R}}\quad\overset{\_}{\Delta_{32}^{R}}\quad{\mathbb{e}}^{- x}}} \right)}} \right\}}}}}$ where ${\Delta_{\quad{jk}}^{\quad R} = \frac{\quad{{s_{\quad k}\quad ɛ_{\quad j}}\quad - \quad{s_{\quad j}\quad ɛ_{\quad k}}}}{\quad{{s_{\quad k}\quad ɛ_{\quad j}}\quad + \quad{s_{\quad j}\quad ɛ_{\quad k}}}}},\quad{\overset{\_}{\Delta_{\quad{jk}}^{\quad R}} = \frac{\quad{s_{\quad k}\quad - \quad s_{\quad j}}}{\quad{s_{\quad k}\quad + \quad s_{\quad j}}}},\quad{s_{\quad k} = \sqrt{\quad{p^{\quad 2}\quad - \quad 1\quad + \quad{ɛ_{\quad k}/\quad ɛ_{\quad 3}}}}}$ ${r = {2\quad d\quad\sqrt{ɛ_{3}}\quad{\xi_{n}/c}}},\quad{\xi_{n} = {2\quad\pi\quad n\quad k_{B}\quad{T/\hslash}}},\quad{ɛ = {ɛ\left( {i\quad\xi_{n}} \right)}},$ k_(B)=1.381×10⁻²³ J/K, T=300 K, c=2.998×10⁸ m/s,

=1.055×10⁻³⁴ J·s, and where d is the plate separation. The subscripts 1 and 2 refer to plates, while subscript 3 refers to an intervening liquid or fluid for this example. It is noted that here the force in this example or embodiment is between the outer layers or plates.

The force between the plates per unit area is plotted in FIG. 2, and is repulsive as expected, from these calculations. Note here that by convention a repulsive force is indicated as positive, although claimed subject matter is, of course, not limited in scope to this convention.

Without limiting the scope of claimed subject matter, another example is provided to illustrate that the sign of the force may, at least in part, depend on a variety of factors, including, here, distance or separation. Consider, for example, the combination LiNbO3-Ethanol-Gold. Dielectric functions from calculation using the two oscillator model are graphed in FIG. 3. It can be seen that ε_(LiNbO3)<ε_(Ethanol)<ε_(Gold) for low frequencies, suggesting repulsive behavior between the plates at larger separations, but we have ε_(Ethanol)<ε_(LiNbO3)<ε_(Gold) for higher frequencies, suggesting attractive behavior between the plates at closer distances. The force is plotted in FIG. 4 and confirms the above discussion.

In this system, as illustrated in the FIGs, there is a crossover from ε₁<ε₃<ε₂ to ε₃<ε₁<ε₂. The force is thus repulsive at large distances, where low imaginary frequencies provide the dominant contribution to the force. Likewise, the force is attractive for smaller separations, where higher frequencies provide the dominant contribution. The zero-point energy here is due at least in part to electromagnetic quantum fluctuations that depend at least in part on the distance between the two interacting plates. If the condition ε₁<ε₃<ε₂ or ε₂<ε₃<ε₁ is satisfied, the zero-point energy per unit area is smaller at larger separation, which means that it is energetically more favorable for a liquid or a fluid, such as Ethanol, for example, to stay inside a gap, such as between LiNbO3 and Gold or between Silica and Gold, rather than outside it. As a consequence, the net force between plates of such materials, for example, is repulsive. It is likewise noted that designing a system, device or the like to at least approximately exhibit a cross-over point, such as previously described, for example, may be a desirable feature of a particular embodiment, depending at least in part on the particular embodiment, for example.

Note that it may be desirable to have surface roughness less than the desired separation distance to avoid contact between surfaces of the plates, for example. Surface roughness may be reduced, for example, by use of polishing, etching techniques (reactive ion etching (RIE), chemical, etc.), ion milling, cleaving along crystal axes, etc. Use of such techniques may be employed to reduce surface roughness to nanometer and/or sub-nanometer scales, for example, if desired.

Although claimed subject matter is not limited in scope in this respect, for an embodiment of a device exhibiting ultra-low static friction, for example, movement may be detected and amplified by employing a variety of different sensors, such as, for example, an actuator, an accelerometer, a gyroscope, a compass and/or a high sensitivity motion sensing device, for example. As simply one example, without limitation, a micro- or a nano-bearing may be used to measure static forces or torques and may find application in situations in which ultra-low static friction is desirable among micro- or nanofabricated mechanical parts. In such devices, forces and torques (e.g. electric, magnetic, gravitational, photon induced, etc.) may be detected that are much smaller than may be identified using traditional sensors, such as sensors which may provide one or more measurements by overcoming static friction at least in part, for example. Thus, embodiments of devices and/or the like employing ultra-low static friction, as previously described, for example, may result in high measurement sensitivity.

FIG. 5 depicts one potential embodiment of a nano- or micro-compass, for example. Of course, claimed subject matter is not limited in scope to this particular embodiment. This can be made, for example, by coating a silica sample with a ferromagnetic material, such as, for example, iron, and putting it, such as 510, silica side down, above a gold surface, such as 520, in which the device is submerged in ethanol. A silica/ethanol/gold combination may lead to a repulsive force between silica and gold and, hence, ultra-low static behavior. A small magnetic field, such as smaller than may be detected from current devices which have static friction, may be applied. Here, this may result in disk rotation due at least in part to ferromagnetic material on the disk. Similarly, a silica/ethanol/gold combination without ferromagnetic material could be used as an accelerometer. A slight change in velocity may allow the disk to slide as a result of ultra-low static friction, for example. Thus, a high sensitivity measurement may be obtained based at least in part on such sliding.

Further, in a variety of possible embodiments, mechanical and/or electromechanical components may be moved or set into motion by extremely small forces. Thus, different devices may be created including, for example, actuators, accelerometers, gyroscopes, compasses, low power MEMS; low power NEMS devices, piezo-like devices, fluidic devices; valves, etc. Many of these devices could be constructed in a similar fashion to their traditional counterparts but be made with materials that lead to a repulsive force, such as previously described. Any material combinations that have dielectric functions which obey the relationship given earlier will display a repulsive dispersion force between outer layers over some distance range and will thus lead to ultra-low static friction behavior. Simple examples include (but are not limited to) any low dielectric function material, e.g. Silicon-dioxide, Calcite, Teflon® or PTFE, etc., submerged in a fluid, e.g. Ethanol, Methanol, Bromobenzene, Cyclohexene, Water, etc., and a metal, e.g. Gold, Silver, Aluminum, Palladium, Platinum etc., or semiconductor, e.g. Silicon, Germanium, GaAs, AlGaAs, etc.

Manufacturing such devices and structures on a relatively small scale, such as, for example, a micron or nano-level scale, may be done using techniques now known or to be later developed, including: Lithography (electron, photon, etc.), Reactive Ion Etching, Chemical Etching, Focused Ion Beams, Crystal Ion Slicing, Silicon-On-Oxide and/or CMOS methods, etc. After structures are created, they may be coated with materials whose dielectric properties are chosen to satisfy conditions for repulsion, as previously discussed, for example. Such techniques include: Evaporation (thermal or otherwise), Sputtering, Spin Coating, Molding, Stamping, Molecular Beam Epitaxy, etc. The devices may likewise be packaged (e.g. PDMS enclosure, Lab On Chip devices, etc.) for transportation and/or use.

In another embodiment of a device within the scope of claimed subject matter, such as one that exhibits ultra-low friction, a small birefringent disk, here, one having a diameter of 40 microns and a thickness of 20 microns, may be employed. Of course, claimed subject matter is not limited in scope to these particular dimensions. However, in this particular embodiment, this disk, illustrated in FIG. 6 as 620, may be made out of quartz or calcite, for example, and placed parallel to a birefringent BariumTitanate (BaTiO3) plate, illustrated in FIG. 6 as 630. In one potential embodiment, as described in more detail later, plate 630 may be immersed in ethanol and disk 620 may be placed on top. In such an embodiment, as a result, a retarded van der Waals force between the two birefringent slabs should be repulsive. Disk 620 may, in this embodiment, float on top of plate 630 at a distance of approximately 100 nm, for example. Weight of disk 620 in this embodiment may therefore be substantially counterbalanced by van der Waals force repulsion. Likewise, in this embodiment, disk 620 is substantially free to rotate, as explained in more detail hereinafter. Likewise, it is noted that this is one particular embodiment and claimed subject matter is not intended to be limited to this particular embodiment. As previously explained, a variety of approaches and techniques may be employed to provide ultra-low friction and this is merely one example embodiment. For example, while in this particular embodiment, the spatial orientation between the plates is illustrated as vertical, this is not necessary and other spatial orientations may be employed. A repulsive force may also be produced in a horizontal orientation, as simply one example.

Continuing with the embodiment mentioned above, however, consider two plates made of uniaxial birefringent materials, the plates being kept substantially parallel at a distance d and immersed inside a medium with dielectric function ε₃, as explained in more detail hereinafter. For sake of simplicity, for this particular embodiment, it is assumed that the two plates are oriented as in FIG. 6, although, of course, claimed subject matter is not limited in scope in this respect. Thus, for this embodiment having this reference system, the z-axis is chosen to be orthogonal to the plates. The optical axis of one of the two crystals, such as the three fold, four fold, or six fold axis of symmetry for rhombohedral, tetragonal, or hexagonal crystals, are aligned with the x-axis. The optical axis of the second crystal is also in the x-y plane, but rotated by an angle with respect to the other, as illustrated in FIG. 6.

For illustrative purposes, if the distance between plates is small enough that the force between them is non-retarded, that is, of van der Waals type, torque may be demonstrated to be inversely proportional to the second power of d and proportional to sin (2θ), as follows: $M = {{- \frac{\hslash\quad\overset{\_}{\omega}\quad S}{64\quad\pi^{2}\quad d^{2}}}{\sin\left( {2\theta} \right)}}$ where S is the surface area and ω is $\overset{\_}{\omega} = {\int_{0}^{\infty}{{\mathbb{d}\xi}\quad{\int_{0}^{\infty}{{\mathbb{d}x} \times \frac{x\quad\left( {\varepsilon_{2 \parallel} - \varepsilon_{2\bot}} \right)\left( {\varepsilon_{1 \parallel} - \varepsilon_{1\bot}} \right)\varepsilon_{3}^{2}{\mathbb{e}}^{- x}}{\left\lbrack {{\left( {\varepsilon_{1\bot} + \varepsilon_{3}} \right)\left( {\varepsilon_{2\bot} + \varepsilon_{3}} \right)} - {\left( {\varepsilon_{1\bot} - \varepsilon_{3}} \right)\left( {\varepsilon_{2\bot} - \varepsilon_{3}} \right){\mathbb{e}}^{- x}}} \right\rbrack^{2}}}}}}$ In a theory which includes retardation effects, as described, for example, in Y. Barash, Ivestiya vuzov, Radiofizika, 12 (1978) 1637, however, it may be difficult to reduce the expression for torque to an analytically solvable expression. Nonetheless, these expressions may be solved numerically. As described in more detail hereinafter, this may be applied to the previously described embodiment, such as the embodiment in which disk 620 and plate 630 are separated by a vacuum.

In such an embodiment, as previously, consider a 20 micron thick, 40 micron diameter disk made out of either quartz or calcite, kept in vacuum substantially parallel to a large BaTiO3 plate at a distance d. To perform a numerical computation of torque experienced by such a disk as a function of θ and d, one may apply dielectric functions of the two plates at imaginary angular frequencies, as previously described. Likewise, the previously described two oscillator model may be applied, although claimed subject matter is not limited in scope in this respect. For this embodiment, parameters that determine the dielectric properties of quartz, calcite, and BaTiO3 in the limit of the two oscillator model are listed in table I of FIG. 9. FIG. 7 is a graph or plot showing calculated dielectric functions at imaginary angular frequencies. Using these functions, the torque was calculated for different angles at d=100 nm, both in a quartz-BaTiO3 and in a calcite-BaTiO3 configuration. Results were obtained for T=300 K, but calculations for smaller temperatures give rise to nearly identical values: at this distance, torque is primarily generated by fluctuations of the electromagnetic field associated with zero-point energy. Materials with less pronounced birefringent properties, such as quartz with respect to calcite, may give rise to a smaller torque and materials with more pronounced birefringent properties may give rise to a larger torque. In this example, the sign of the torque obtained for the quartz-BaTiO3 configuration is opposite to the one obtained for calcite-BaTiO3. This behavior may be understood from FIG. 7, for example. A dominant contribution to torque comes from angular frequencies in the region where the dielectric tensor perpendicular to the optical axis is greater than the dielectric tensor parallel to the optical axis. The minimum zero-point energy corresponds to the situation in which the axes of the dielectric tensors with larger values of the dielectric function are aligned.

As previously discussed, in an embodiment in which a quartz or calcite disk is above a BaTiO3 plate immersed in ethanol, the retarded van der Waals force between the disk and the plate is repulsive; thus, if the disk is placed on top of the plate, this repulsion may be used to substantially counterbalance the weight of the disk, for example. In liquid ethanol, therefore, the disk would float substantially parallel on top of the plate at a small distance. The static friction between the two birefringent plates in this particular embodiment would be ultra-low, and the disk would be free to rotate suspended in bulk liquid. Likewise, the dynamic friction should also be ultra-low for this particular embodiment. Furthermore, viscous drag may also be reduced in other embodiments by choosing a less viscous fluid or by modifying the surface geometry of the interacting bodies, for example, although claimed subject matter is not limited in scope in this respect.

For distances shorter than a few nanometers, the force is attractive. However, at larger distances, where retardation effects are non-negligible, the force becomes repulsive. From Lifshitz's theory for isotropic materials, it is possible to show that the force between two plates with dielectric functions ε₁ and ε₂ immersed in a medium with dielectric function ε₃ is repulsive if, for imaginary frequencies, ε₁<ε₃<ε₂ or ε₂<ε₃<ε₁, and it is attractive in other cases. In this particular embodiment, there is a crossover from ε₁<ε₁<ε₂ to ε₃<ε₁<ε₂ at about 5×10¹⁵ rad/s. The force is thus repulsive at large distances, where low imaginary frequencies primarily contribution to the force, and attractive for smaller separations, where higher frequencies are more relevant, as described in a previous embodiment. Zero-point energy from electromagnetic quantum fluctuations depends at least in part on the distance between interacting plates. Assuming, for example, one of the relationships just described applies, zero-point energy per unit area is smaller at larger separation, which means, as also previously described, that it is energetically more favorable for a liquid or fluid to stay inside a gap, such as between a plate and disk, for example. As a consequence, the net force is repulsive.

For this particular embodiment, the net weight of the disk immersed in ethanol may be given by: F _(gr) =−Sh(ρ_(disk)−ρ_(ethanol))g in which S is the surface of the disk, h is its thickness, ρ_(disk) is the mass density of either quartz (2643 kg/m3) or calcite (2760 kg/m3), ρ_(ethanol) is the mass density of ethanol (789 kg/m3), and g is 9.81 m/s². In these particular embodiments, the equilibrium separation is about 100 nm. Of course, claimed subject matter is not limited in scope to this particular separation or to this particular configuration. Likewise, this distance may be tailored by a variety of techniques, such as by changing the thickness of the disk to provide one simple example of one possible change. As suggested previously, while some embodiments may not necessarily exhibit a cross-over; likewise, in some embodiments, it may be desirable to have a cross-over and/or have the capability to affect at least somewhat its location.

A schematic view of one embodiment, as previously described, is shown in FIG. 8. A 40 micron diameter, 20 micron thick disk made out of quartz or calcite is placed on top of a BaTiO3 plate immersed in ethanol. The optical axes of birefringent crystals are oriented as in FIG. 6. A disk should levitate approximately 100 nm above the plate and should be free to rotate. For example, a 100 mW laser beam may be collimated onto the disk to rotate it by a transfer of angular momentum of light, although claimed subject matter is, of course, not limited in scope to the laser or power of the laser employed. A shutter may block the beam to interrupt the light-induced rotation. Using a laser, for example, one may rotate the disk. After the laser beam is shuttered, the disk may be free to rotate back towards the configuration of reduced energy.

Likewise, disks with different dimensions and geometries may be constructed to rotate faster. Suitably engineered samples could also result in additional configurations. For example, a thick layer of lead could be deposited on a portion of a disk to make it heavier: the disk may float at a smaller distance, where the magnitude of the driving torque would be larger, for example. Furthermore, use of a different liquid with optical properties similar to ethanol but with a smaller viscosity may increase the angular velocity of the disk, as another example.

It will, of course, be understood that, although particular embodiments have just been described, claimed subject matter is not limited in scope to a particular embodiment or implementation. For example, one embodiment may be in hardware, such as implemented to operate on a device or combination of devices, for example, whereas another embodiment may be in software. Likewise, an embodiment may be implemented in firmware, or as any combination of hardware, software, and/or firmware, for example. Likewise, although claimed subject matter is not limited in scope in this respect, one embodiment may comprise one or more articles, such as a storage medium or storage media. This storage media, such as, one or more CD-ROMs and/or disks, for example, may have stored thereon instructions, that when executed by a system, such as a computer system, computing platform, or other system, for example, may result in an embodiment of a method in accordance with claimed subject matter being executed, such as one of the embodiments previously described, for example. As one potential example, a computing platform may include one or more processing units or processors, one or more input/output devices, such as a display, a keyboard and/or a mouse, and/or one or more memories, such as static random access memory, dynamic random access memory, flash memory, and/or a hard drive.

In the preceding description, various aspects of claimed subject matter have been described. For purposes of explanation, specific numbers, systems and/or configurations were set forth to provide a thorough understanding of claimed subject matter. However, it should be apparent to one skilled in the art having the benefit of this disclosure that claimed subject matter may be practiced without the specific details. In other instances, well-known features were omitted and/or simplified so as not to obscure claimed subject matter. While certain features have been illustrated and/or described herein, many modifications, substitutions, changes and/or equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and/or changes as fall within the true spirit of claimed subject matter. 

1. An apparatus comprising: a device exhibiting ultra-low friction.
 2. The apparatus of claim 1, wherein said device comprises a device exhibiting ultra-low dynamic friction.
 3. The apparatus of claim 2, wherein said device exhibits ultra-low dynamic friction at least in part by substantially counterbalancing net weight of a first object with van der Waals repulsion between the first object and a second object.
 4. The apparatus of claim 2, wherein said device comprises a device exhibiting ultra-low static friction.
 5. The apparatus of claim 4, wherein said device exhibits static friction below a value, wherein said value is ultra-low.
 6. The apparatus of claim 4, wherein said device exhibits ultra-low static friction at least in part by substantially counterbalancing net weight of a first object with van der Waals repulsion between the first object and a second object.
 7. The apparatus of claim 6, wherein the spatial relationship between the first object and the second object is not necessarily perfectly vertically oriented.
 8. The apparatus of claim 6, wherein said objects comprise metallic material.
 9. The apparatus of claim 6, wherein said objects comprise at least partially birefringent material.
 10. The apparatus of claim 9, wherein one of said objects comprises a disk and the other of said objects comprises a plate.
 11. The apparatus of claim 10, wherein said disk is around 20 microns thick.
 12. The apparatus of claim 10, wherein said disk has a diameter of around 40 microns.
 13. The apparatus of claim 10, wherein said objects are separated by a fluid.
 14. The apparatus of claim 13, wherein said fluid comprises ethanol.
 15. The apparatus of claim 10, wherein said disk is substantially free to rotate.
 16. The apparatus of claim 6, wherein said objects are separated by a relatively small distance sufficient to maintain the counterbalancing.
 17. The apparatus of claim 16, wherein said distance is sufficiently small so that van der Waals forces between said objects are not negligible.
 18. The apparatus of claim 16, wherein said distance is sub-micron.
 19. The apparatus of claim 1, wherein said device is incorporated into at least one of the following: an actuator; an accelerometer; a gyroscope; a compass and/or a high sensitivity sensor.
 20. An apparatus comprising: a device made of materials selected so that van der Waals forces between at least some of said materials are repulsive.
 21. The apparatus of claim 20, wherein said materials have a respective dielectric function, ε_(N), in which N is 1, 2, 3 such that for imaginary frequencies ε₁<ε₃<ε₂; and the material corresponding to dielectric function ε₃ corresponds to a fluid separating the other materials.
 22. The apparatus of claim 20, wherein said materials have a respective dielectric function, ε_(N), in which N is 1, 2, 3 such that for imaginary frequencies ε₂<ε₃<ε₁; and, the material corresponding to dielectric function ε₃ corresponds to a fluid separating the other materials.
 23. The apparatus of claim 20, wherein said repulsive van der Waals forces substantially counterbalance one or more other forces in said device.
 24. The apparatus of claim 23, wherein said one or more forces comprise net weight of a portion of solid material.
 25. The apparatus of claim 20, wherein said materials include at least one of the following: quartz; calcite; and/or barium titanate.
 26. A method of producing ultra-low friction comprising: combining materials so that van der Waals forces between at least some of said materials are repulsive.
 27. The method of claim 26, wherein said materials have a respective dielectric function, ε_(N), in which N is 1, 2, 3 such that for imaginary frequencies ε₁<ε₃<ε₂; and the material corresponding to dielectric function ε₃ corresponds to a fluid separating the other materials.
 28. The method of claim 26, wherein said materials have a respective dielectric function, ε_(N), in which N is 1, 2, 3 such that for imaginary frequencies ε₂<ε₃<ε₁; and, the material corresponding to dielectric function ε₃ corresponds to a liquid separating the other materials.
 29. The method of claim 26, wherein said repulsive van der Waals forces substantially counterbalance one or more other forces in said device.
 30. The method of claim 29, wherein said one or more forces comprise net weight of a portion of solid material.
 31. An apparatus comprising means for producing ultra-low static friction and a sensor to sense said ultra-low static friction.
 32. The apparatus of claim 31, wherein said means for producing ultra-low static friction comprises means for substantially counterbalancing net weight of a first object with van der Waals repulsion between the first object and a second object.
 33. The apparatus of claim 32, wherein said objects comprise metallic material. 